Accretion, Primordial Black Holes and Standard Cosmology

Primordial Black Holes evaporate due to Hawking radiation. We find that the evaporation time of primordial black holes increase when accretion of radiation is included.Thus depending on accretion efficiency more and more number of primordial black holes are existing today, which strengthens the idea that the primordial black holes are the proper candidate for dark matter.Comment: 11 pages, 3 figure

Brans-Dicke Theory and primordial black holes in Early Matter-Dominated Era

We show that primordial black holes can be formed in the matter-dominated era with gravity described by the Brans-Dicke theory. Considering an early matter-dominated era between inflation and reheating, we found that the primordial black holes formed during that era evaporate at a quicker than those of early radiation-dominated era. Thus, in comparison with latter case, less number of primordial black holes could exist today. Again the constraints on primordial black hole formation tend towards the larger value than their radiation-dominated era counterparts indicating a significant enhancement in the formation of primordial black holes during the matter-dominaed era.Comment: 9 page

Magnetic properties of pure and Eu-doped hematite nanoparticles

Nanoparticles (NPs) of pure and Eu-doped hematite were prepared by a wet chemical technique; their structure, size and morphology were determined by XRD and transmission electron microscopy. The magnetic properties were measured in the 6-320 K temperature range by vibrating-sample magnetometry. Pure hematite NPs exhibit a pseudo-cubic shape with a size of about 74 nm; addition of trivalent Eu cations in different amounts (Eu/Fe atomic ratios 2.4 %) brings about a definite change in particle morphology with the development of rice-grain like NPs with aspect ratios of about 2.8. Trivalent Eu cations act as magnetic defects making the overall antiferromagnetic arrangement of hematite host less robust. A large defect magnetism arises below the Morin transition temperature. The resulting uncompensated moments on NPs (mostly arising from the NP cores) behave superparamagnetically before undergoing single-particle blocking at about 40 K. Instead, uncompensated moments in pure hematite NPs mostly occur at the NP surface and lead to standard defect ferromagnetism. Above the Morin temperature, the usual spin-canted ferromagnetism is observed in all samples, although it is somewhat inhibited by Eu additio